The invention relates to a method for the dressing of a multi-thread grinding worm by means of a dressing roll, wherein the grinding worm has at least two screw channels which are arranged parallel to another, which screw channels extend helically around an axis of the grinding worm and wherein the dressing roll has at least two adjacent dressing profiles which are arranged along an axis of the dressing roll, wherein the dressing profiles of the dressing roll are guided simultaneously through adjacent screw channels of the grinding worm during the dressing of the grinding worm.
Normally, a dressable multi-thread grinding worm is used at the machining of gearings, cycloids or rotor profiles with generative tools. In turn the dressing of the grinding worm takes place with a one or multi groove dressing roll.
The dressing with a single groove dressing roll (single row dressing) takes place by a plurality of single infeeds with one respective machining stroke in each channel and is repeated after parting (i.e. after the profile of the dressing roll is inserted in the next channel of the multi-thread grinding worm) in each channel of the grinding worm.
The use of a multi-groove dressing roll achieves a time advantage compared with a single-groove roll because during dressing several threads (i.e. grooves) of the grinding worm can be dressed simultaneously and so the parting in the single threads of the grinding worm can be reduced or can be omitted at all.
Due to cost reasons always a time-optimized dressing is aimed for. For example if a 3-grooved dressing tool (dressing roll) is used for the production of a 3-thread grinding worm the partition process is omitted totally because all three threads or grooves of the grinding worm can be dressed simultaneously. If the number of threads is higher than the number of grooves of the dressing roll is must be parted accordingly to dress all threads of the grinding worm.
It is the aim of the dressing that finally a grinding worm is obtained which is free of failures as possible at which all threads are distributed exact equally around the circumference and do not differ from another with respect to their geometry.
The dressing tool is designed in such a manner that all grooves (i.e. all dressing profiles) create the same geometry at or in the worm thread. Due to the design of the multi-groove dressing roll for a predetermined tool diameter, thus due to the given fixed geometry, due to the defects in manufacturing of the dressing roll and due to the fact that not all threads of the grinding worm are dressed with the same groove (i.e. with the same dressing profile) geometry defects in the grinding worm are created, thus in the grinding tool. Those defects are transferred systematically at first to the tool and then to the work piece at the subsequent grinding process.
The dressing occurs normally not axially parallel but in the lead angle of the grinding worm. Because the lead angle changes with smaller becoming diameter of the grinding worm also the created geometry of the grinding worm is changing due to the fixed geometry of the dressing tool and due to the fact that not all grooves (dressing profiles) of the dressing roll are arranged in the pivot center of the grinding worm.
This is substantially the reason that multi-groove dressing tools cannot be used for all module ranges of a gearing. A bigger module means a bigger lead angle; thus the grooves of the dressing roll, which are not arranged in the pivot center of the grinding worm, create bigger deviations.
The single-groove dressing tool creates always a higher quality than the multi-groove dressing but requires more time for dressing and thus higher costs.